This invention relates to a char-protective coating for flexible base materials such as pressure sensitive adhesive tapes used to wrap and protect capacitors, coils and other electrical/electronic components in the event of a flaming environment.
Pressure sensitive adhesive tapes used to wrap and protect capacitors and coils are normally formed from thin polyester film backings and an acrylic or rubber/resin pressure sensitive adhesive to take advantage of the physical, chemical and electrical properties that such a composite affords. Thus, such composites are thin and flexible but strong, they afford good chemical and solvent resistance, they have good dielectric properties and they are non-corrosive. The problem with such polyester tapes, whether the pressure sensitive adhesive itself is formulated to be flame retardant or not, is that when subjected to flame, the polyester, which is the outermost surface and is thereby directly subjected to the flame, and/or pressure sensitive adhesive melts and drips usually as a flaming mass. If applied to a capacitor, the burning tape will melt and drip or burn away leaving the capacitor, which is by nature also composed largely of polyester film, exposed to the source of flame. The flaming drips can also ignite other parts of the electronic assembly containing the electrical component.
Flame retardant tapes are also known composed of inherently flame retardant backings such as Kapton, a trademark of DuPont, Telfon, also a trademark of DuPont, or fiberglass, such backings being coated with pressure sensitive adhesives. These tapes meet the requirements of UL 510 for flame retardancy and also meet the requirements of UL 1414 which is a test of an actual wrapped capacitor for flame retardancy. However, Kapton and Teflon are much more expensive than polyester film although such materials are now used on capacitors and coils to meet the standards of UL 1414. Fiberglass is also more expensive than polyester film and suffers from poor comformability when wrapping.
The flame retardant polyester tapes taught in U.S. Pat. No. 4,061,826 meet the requirements of UL 510 but do not meet the requirements of UL 1414 when tested on an actual capacitor because the polyester melts and drips, forming flaming drips and burns away exposing the polyester-foil inner wrappings of the capacitor.
It is an object of this invention to provide a means of making conformable, low cost commonly used film, such as polyester, flame retardant so that it will not only pass the requirements of UL 510, but more importantly, the requirements of UL 1414 where the actual component is tested.
It is a further object of the present invention to make a tape that will not melt or drip away from the electrical/electronic component it was designed to protect when exposed to flame.
It is another object of this invention to make a tape that will continue to protect the electrical/electronic component even though burned in a flame.